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首页> 外文期刊>Journal of Asian earth sciences >Post-collisional Plio-Pleistocene shoshonitic volcanism in the western Kunlun Mountains, NW China: Geochemical constraints on mantle source characteristics and petrogenesis
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Post-collisional Plio-Pleistocene shoshonitic volcanism in the western Kunlun Mountains, NW China: Geochemical constraints on mantle source characteristics and petrogenesis

机译：中国西北昆仑山碰撞后的上新世更新世火山岩火山作用：地幔来源特征和岩石成因的地球化学约束

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Major and trace element, Sr-Nd-Pb isotope and mineral chemical data are presented for post-collisional late Cenozoic shoshonitic volcanic rocks from the western Kunlun Mountains, NW China. They are distributed in two approximately E-W striking sub-belts, with the lavas in the southern sub-belt having been generated earlier than those in the northern sub-belt. The mineralogy of the rocks reflects crystallization from moderate temperature magmas (700-1000 ℃) with high oxygen and water fugacities. They are geochemically characterized by relatively low TiO_2, Al_2O_3 and FeO and high alkalies coupled with very high contents of incompatible element concentrations. Remarkably negative Nb, Ta and Ti anomalies are displayed on primitive mantle-normalized incompatible element patterns. In addition, they show a relatively broad range of low ε_(Nd) (-1.8 to -8.7) at more restricted ~(87)Sr/~(86)Sr ratios (0.7081-0.7090). Pb isotopes are characterized by a range of ~(207)Pb/~(204)Pb (15.48-15.74) and ~(208)Pb/~(204)Pb (38.30-39.12) ratios at relatively invariant ~(206)Pb/~(204)Pb (18.60-18.83) values, except one sample with a ratio of 18.262, leading to near-vertical arrays. The lavas from the northern sub-belt have relatively high ~(87)Sr/~(86)Sr ratios. All lavas have extremely high La/Yb ratios, probably reflecting that the magmas were derived from a metasomatized lithospheric mantle source containing phlogopite-hornblende garnet peridotite affected by subducted sediments and hydrous fluids, rather than from a depleted asthenopheric mantle source or mantle plume source. However, the lavas from the southern sub-belt were derived from a lower degree of melting of more highly metasomatized sub-lithospheric mantle in comparison with those from the northern sub-belt. Processes responsible for partial melting of metasomatized lithospheric mantle and post-collision magmatism in the western Kunlun could be a consequence of continuously conductive heating of upwelling, hot asthenospheric mantle following the delamination subsequent to thickening, which is consistent with the spatial and temporal geochemical variations in shoshonitic rocks in Tibet.
机译：给出了中国西北昆仑山碰撞后新生代晚新生代火山岩的主要和微量元素，Sr-Nd-Pb同位素和矿物化学数据。它们分布在两个近似E-W的子带中，南部子带中的熔岩比北部子带中的熔岩产生得早。岩石的矿物学特征反映了中等温度岩浆（700-1000℃）具有高氧和水逸度的结晶。它们的地球化学特征是TiO_2，Al_2O_3和FeO相对较低，碱金属含量较高，且不相容元素浓度很高。 Nb，Ta和Ti异常显着为负，显示在原始地幔归一化的不兼容元素图案上。此外，它们在〜（87）Sr /〜（86）Sr比（0.7081-0.7090）受更严格的限制时，显示出较低的ε_（Nd）（-1.8至-8.7）相对较大的范围。 Pb同位素的特征是〜（207）Pb /〜（204）Pb（15.48-15.74）和〜（208）Pb /〜（204）Pb（38.30-39.12）之比在相对不变的〜（206）Pb范围内/（204）Pb（18.60-18.83）值，但比率为18.262的一个样本除外，从而导致近乎垂直的阵列。北部亚热带的熔岩具有较高的〜（87）Sr /〜（86）Sr比。所有熔岩的La / Yb值都非常高，这可能反映出岩浆来自交代的岩石圈地幔源，其中含有受俯冲沉积物和含水流体影响的金云母-角闪石石榴石橄榄岩，而不是贫化的软流层地幔源或地幔柱源。然而，与北部子带相比，南部子带的熔岩是由高度交代的岩石圈以下地幔融化程度较低而形成的。昆仑西部地区交代岩石圈地幔部分熔融和碰撞后岩浆作用的过程可能是由于增厚后的分层分层之后对上升流，热软流层地幔进行连续传导加热的结果，这与中空的地球化学变化一致。西藏的岩石岩石。

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